The present invention relates to motion suppression techniques in video systems, and more particularly to a field motion suppression technique in interlaced video displays which preserves vertical resolution of a resulting motion suppressed video frame.
In commercial television systems, such as NTSC and PAL, each video frame has two interlaced fields. If the lines within a frame are numbered sequentially from top to bottom, then the odd numbered lines are from the odd field and the even numbered lines are from the even field. If an object is moving rapidly, it may appear in different locations within each field. Certain devices, such as video cassette recorders, still stores, etc, are capable of "freezing" a single frame of a video signal. An object in motion within the picture represented by the single frame appears to flicker within two areas of the frame as the two interlaced fields are alternately displayed. An extreme illustration of this effect is shown in FIG. 1 where a stationary rectangular object and a moving ball are pictured. As the two fields are continuously redisplayed each of the images of the ball appears to flicker. What is desired is a display with the ball either in one position or the other.
A simple prior art solution is to simply pick one of the two fields and continuously redisplay it for both fields. For example if the odd field is chosen, then line 1 is displayed in alternate fields as lines 1 and 2, line 3 is displayed in alternate fields as lines 3 and 4, etc. This approach fills in the missing lines, but produces rather odd looking images because it tends to make the most well defined edges look jagged.
A better approach involves averaging. Assuming that the odd field is once again chosen for display, lines in the even field are produced by averaging. A pixel to be displayed on line 2 is obtained by averaging the pixel above on line 1 with the pixel below on line 3. This produces a more acceptable looking picture than the simple previous approach, but there is still a visible loss of vertical resolution.
In both of the above approaches vertical resolution is sacrificed within the entire picture image, even though most of the image may be stationary between the two fields. Ideally stationary objects within the image should not suffer a loss of vertical resolution along with those objects that are in motion.
Therefore what is desired is a method of detecting motion between the two consecutive fields selected to produce a video frame and change pixel values only where motion is detected to preserve vertical resolution for stationary objects.